I've developed an ASP.NET 2.0 website, at the place I work at, that
needs to support both web accounts and windows accounts, (via A.D. -
it's complicated so I won't bore you). Therefore I've extended the
SqlMembershipProvider to include A.D. support via custom code. The
problem I have is that, whilst it works on my local test server, when
the website's published to a 'testing' server the A.D. code doesn't
work at all.

My requirement is to find the GUID for the current user's account, (so
it can be looked up via a separate system, which I can't change). The
basic code I use to get this data is;

// See if there's a windows log-in account entry for the current user.
WindowsIdentity objWindowsIdentity = WindowsIdentity.GetCurrent();
if (objWindowsIdentity != null)
{
  // Now look it up via A.D. to find their corresponding account
there.
  //  -> First set-up the searching options to find this user.
  DirectoryEntry objParentDirEntry = new DirectoryEntry(...);
  //if (objParentDirEntry != null)
  //{
     // -> As the windows account name will be '{network}\
{username}', extract the actual name to locate.
     string strUsername = objWindowsIdentity.Name.Split('\\')[1];
     DirectorySearcher objSearcher = new
DirectorySearcher(objParentDirEntry,
String.Format("(sAMAccountName={0})", strUsername));
     SearchResult objResult = objSearcher.FindOne();
     if (objResult != null)
     {
        // -> Their A.D. information has been successfully found, so
return the results.
        pobjDirEntry = objResult.GetDirectoryEntry();
     }
  //}
}
Where the 'pobjDirEntry' is the DirectoryEntry used for finding the
GUID.

The problem is I get the following error when the search is performed:
System.Runtime.InteropServices.COMException (0x80072020): An
operations error occurred.
  at System.DirectoryServices.DirectoryEntry.Bind(Boolean
throwIfFail)
  at System.DirectoryServices.DirectoryEntry.Bind()
  at System.DirectoryServices.DirectoryEntry.get_AdsObject()
  at System.DirectoryServices.DirectorySearcher.FindAll(Boolean
findMoreThanOne)
  at System.DirectoryServices.DirectorySearcher.FindOne()
  ...

Can someone point out what I've done wrong, or a better way of
performing the above? Or simply explain why I'm getting the error, and
what I can do to fix it?
Everything I've read about the error says the search criteria is
wrong, but it works locally and the details it uses , as far as
everyone I've spoken to at my company is concerned, are correct.
Otherwise it's that the user's security isn't high enough, but no-one
says what it *should* be. Can someone explain it to me

Thanks in advance,
Paul